| Date | Tue, 04 Jun 2013 19:22:25 +0200 | From | Willy Tarreau <> | Subject | [ 055/184] KVM: x86: fix for buffer overflow in handling of |
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2.6.32-longterm review patch. If anyone has any objections, please let me know.
------------------ MSR_KVM_SYSTEM_TIME (CVE-2013-1796)
From: Andy Honig <ahonig@google.com>
commit c300aa64ddf57d9c5d9c898a64b36877345dd4a9 upstream.
If the guest sets the GPA of the time_page so that the request to update the time straddles a page then KVM will write onto an incorrect page. The write is done byusing kmap atomic to get a pointer to the page for the time structure and then performing a memcpy to that page starting at an offset that the guest controls. Well behaved guests always provide a 32-byte aligned address, however a malicious guest could use this to corrupt host kernel memory.
Tested: Tested against kvmclock unit test.
Signed-off-by: Andrew Honig <ahonig@google.com> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com> Cc: Ben Hutchings <ben@decadent.org.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Willy Tarreau <w@1wt.eu> --- arch/x86/kvm/x86.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 271fddf..e24e9ce 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -925,6 +925,11 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data) /* ...but clean it before doing the actual write */ vcpu->arch.time_offset = data & ~(PAGE_MASK | 1); + /* Check that the address is 32-byte aligned. */ + if (vcpu->arch.time_offset & + (sizeof(struct pvclock_vcpu_time_info) - 1)) + break; + vcpu->arch.time_page = gfn_to_page(vcpu->kvm, data >> PAGE_SHIFT); -- 1.7.12.2.21.g234cd45.dirty
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